The murine H-2 transplantation alloantigens are cell membrane integrated glycoproteins carrying the antigenic determinants involved in tissue graft rejection. The molecular expression of these antigens is controlled by an unusually complex and polymorphic genetic region in the IX linkage group. The long term objective of the proposed research project is to describe the molecular architecture of these membrane specific polymorphic gene products in order to understand the organization and expression of the H-2 genes as well as the structural and functional properties associated with the antigens themselves, as integral components of the plasma membrane. Our major effort has been directed towards the use of radiochemical sequencing methodology to determine the total amino acid sequence of the H-2Kb gene product. CNBr peptides have been isolated from this molecule, characterized, and aligned. Sequence analysis of the NH2-terminal ends of these five major fragments has been carried out. Studies also have been carried out on the structure of the mutants of the H-2Kb series and of the mutant H-2Dda. Full peptide mapping studies have shown in all cases that the mutant glycoprotein is different from the parent glycoprotein. In the case of the H-2Kb series only small differences were noted as compared with the parent H-2Kb. In the case of the H-2Dda mutant larger differences were noted as compared to the parent H-2D glycoprotein.